A copolymer of tributyltin methacrylate with methyl methacrylate or the like has bee used for the hydrolytic self-polishing polymer in a ship bottom paint. This copolymer is hydrolyzed in water to release bistributyltin oxide, and the hydrolyzed part of the polymer turns into a carboxylic acid which is soluble in water, and therefore, this part dissolves in water to constantly expose an active surface.
However, the bistributyltin oxide released during the hydrolysis is highly toxic, and this compound pollutes the water into which it released. Accordingly, there is a growing concern for the adverse influence on the ecosystem.
Various tin-free polymers have been developed in view of such situation, and Japanese Patent No. 3053081 and U.S. Pat. No. 4,593,055 propose replacement of the bistributyltin methacrylate with a trialkylsilyl (meth)acrylate such as tributylsilyl methacrylate or triisopropylsilyl acrylate, and copolymerization of such trialkylsilyl (meth)acrylate with the alkyl methacrylate.
However, in the case of the copolymer of the trialkylsilyl (meth)acrylate and the alkyl methacrylate, the compound released by the self-polishing of the polymer by the hydrolysis is a trialkyl silanol which does not have the effect of suppressing the attachment of marine organisms, and also, the polymer itself does not have the effect of suppressing the attachment of marine organisms. Accordingly, and simultaneous use of a biocide is required to suppress the attachment of the marine organisms.
A hydrolytic self-polishing polymer which can do away with or reduce the biocide is disclosed in JP-A 63-253090. This polymer is prepared by using a siloxy group-containing silyl (meth)acrylate compound such as tris(trimethylsiloxy)silyl (meth)acrylate for the copolymerization with the alkyl methacrylate. This siloxy group-containing polymer has a reduced surface free energy, and this results in the reduced attachment of the marine organisms to the surface to allow prevention of the marine organism attachment with no or reduced amount of the biocide. This siloxy group-containing polymer also allows constant exposure of the active polymer surface by hydrolytic self-polishing of the polymer, and the attachment of the marine organisms is constantly suppressed. However, this siloxy group-containing silyl (meth)acrylate compound is hydrolyzed at an excessively high speed, and the anti-fouling effect was not sustainable due to the quick dissolution of the polymer. Accordingly, there is a demand for a siloxy group-containing silyl (meth)acrylate compound having a higher stability for the hydrolysis.